Error control coding introduces controlled redundancy into the transmitted messages that is exploited at the receiver to correct transmission errors that are introduced by the noisy channel, commonly called forward error correction. An error control code may also be used for error detection in schemes that employ automatic repeat request (ARQ) strategies. There are many different types of error correcting codes, but historically they have been classified into block codes and convolutional codes. This chapter starts with an introduction to block coding and decoding techniques. This is followed by convolutional codes and the Viterbi algorithm for decoding convolutional codes. Trellis coded modulation is also considered for bandwidth efficient nonbinary signaling schemes. Afterwards, the performance analysis of convolutional and trellis codes on AWGN channels is considered. Most error control codes are designed for memoryless channels and block and convolutional interleavers are described that are useful for coded communication on channels with memory such as land mobile radio channels. Finally, the chapter concludes with a discussion of automatic repeat request (ARQ) schemes.